1. Field of the Invention
The invention relates to an electrical scanning probe microscope apparatus, and more particularly to an electrical scanning probe microscope apparatus comprising an atomic force microscope equipped with a long-wavelength laser source.
2. Description of the Related Art
Scanning probe microscopes (SPMs) providing very high resolution images of various surface properties are typically employed as a means of measuring surface topography and corresponding electrical property analysis. Different types of electrical properties can be measured such as, conductivity, voltage, capacitance, resistivity, current, and others. Accordingly, many different SPM techniques may be used when measuring electrical properties. For example, SPM techniques that may be used for synchronously providing electrical signals corresponding to topographic images comprise scanning capacitance microscopy (SCM), scanning spreading resistance microscopy (SSRM), Kelvin force microscopy (KFM) and conductive atomic force microscopy (C-AFM).
The scanning capacitance microscope (SCM) apparatus works by scanning a tiny tip over the surface of a sample being imaged, while synchronously measuring the electrical properties of the sample. A typical SCM apparatus comprises an atomic force microscope (AFM) and an ultra-high frequency (UHF) resonant capacitance sensor can synchronously provide a two-dimensional image. The AFM acquires surface topographic images, and the UHF resonant capacitance sensor provides a synchronous two dimensional differential capacitance images. The AFM typically comprises a cantilever and a conductive probe at the free end of the cantilever. In most AFMs the position of the cantilever is detected with optical techniques. A red laser beam (670 nm) reflected off the back of the cantilever onto a position-sensitive photo-detector is adapted to detect the position of the cantilever. The AFM can thus generate topographic images. However, photoperturbations, such as the photovoltaic effect and the high-level carrier injection effect induced by stray light of the AFM red laser beam lead to distorted differential capacitance (dC/dV) profiles and hence perturb the contrast of SCM images.
According to recent research, narrow band-gap semiconductors, such as Si, GaAs, InP or others, suffer from the aforementioned photoperturbations. The photoperturbations induced by the AFM laser beam not only affect the image contrast of SCM images, but also reduce the accuracy of the determination of the carrier concentration distribution. Solutions to these problems have been long sought but thus far have eluded those skilled in the art.